This invention relates to glue bond testing, and more particularly to apparatus for testing the integrity of the glue bond of a flap of a paperboard carton or container.
In the packaging industry and particularly in the business of automatic filling and packaging of canned or bottled soft drink, beer and the like, there is a need to be able to check the integrity of the glue bond of the paper end flaps of paperboard cartons, and particularly the cartons which contain canned and bottled beverages. Typically, the cartons which contain such beverages are formed of coated, unbleached board stock, and the coating is typically a clay coating to provide a superior surface for printing. This surface must also provide a satisfactory glue bonding cite, compatible with on-line gluing operations forming a part of the filling and packaging of such products.
Typically, the integrity of the glue joint formed between the end flaps is tested by hand. This is done by taking a filled carton off the line and manually pulling one of the end flaps away, while subjectively noting how difficult it is to pull the flap. Also, the interface between the previously joined flaps is viewed to determine the extent to which fiber tear has been produced, that is, the extent to which the board itself has been caused to separate, rather than merely part across the glue interface. Those in industry who customarily practice testing by manually opening a carton have commonly viewed splitting of the coating, as distinguished from fiber tear, as an indication of a poor internal bond strength.
Recent investigations have concluded that the extent to which fiber tear is exposed is not necessarily an indication of the integrity or actual strength of the glue bond at the end flaps of a paperboard carton. Thus, depending on the surface characteristic of the board and other characteristics of the fiber and the glue, a glue bond separation along or through the glue interface may not be an indication of an inadequate glue bond.
The manual test of pulling a carton open by hand, presently used by many of the carton converters and product manufacturers, involves a substantial subjective element, making this evaluation difficult to interpret, and usually not repeatable. Prior art glue bond testers, to eliminate the subjective element, typically involve the testing of a specially prepared laboratory glue bond joints in a laboratory instrument, to provide an indication of the joint which can be expected in actual use. Thus, the U.S. patents of Skundberg, 3,396,578 issused Aug. 13, 1968 and Liebrenz et al, 4,080,825 issued Mar. 28, 1978 exemplify glue bond testers in which specially prepared strips are formed, the bonds of which are tested by the apparatus shown in those patents. These instruments are not adapted to the testing of production cartons taken off line for quality control inspection.
There is accordingly a need for apparatus which provides a quantitative evaluation of the opening force of a glued or bonded carton flap, and a need particularly for such an instrument which permits standardization of testing parameters and techniques, so that direct comparisons can be made between tests.